Summary of Work: The pathogenesis of degenerative diseases of aging involve the loss of important functional cell types . Apoptosis is a form of programmed cell death that is responsible for the elimination of many cell types during development. We are carrying out studies to determine the importance of apoptosis in the biology of the chondrocyte. We have optimized an in situ procedure for the detection of apoptotic cells to cartilage. We have made the exciting discovery that chondrocytes in the articular cartilage of mature animals are undergoing apoptosis and that the number of apoptotic cells increases with age. This finding supports the concept that loss of chondrocytes by programmed cell death may contribute to the development of age-associated degenerative cartilage disease. Over the past year we have conclusively demonstrated that Bcl-2 ( an anti-apoptotic protein) plays a critical role in the regulation of apoptosis in articular chondrocytes by carrying out both in vitro and in vivo studies. These studies include overexpression of both sense and anti-sense transcripts of Bcl-2 in chondroocytes which protects or sensitizes the cells to apoptosis respectively. In addition we have measured the level of Bcl-2 and Bax (a pro-apoptotic signal) in human chondrocytes and have shown that the ratio of Bcl-2/Bax decreases when the cells are induced to undergo apoptosis. Finally we have demonstrated that Bcl-2 plays a role in regulating chondrocyte apoptosis in vivo by establishing that there is an increased incidence of chondrocyte apoptosis in the articular cartilage of animals with reduced expression of Bcl-2. In related work we have solid evidence to suggest that Bcl-2 may play a role in regulating the expression of aggrecan (the major proteoglycan of cartilage) independent of its role in regulating apoptosis. These studies establish a solid foundation for testing the hypothesis that decreased Bcl-2 expression with aging may